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The distributed generator based on power electronic converters has no inherent inertial response like that from the rotating mass of the conventional synchronous generator. The control scheme of Virtual Synchronous Generator (VSG) is anticipated to improve the distributed generator system stability by imitating the behavior of the synchronous generator including the system inertia. Unlike a real synchronous...
The increasing implementation of Distributed Generation (DG) in the distribution grids creates new challenges in controlling the voltage profile. If the DG production exceeds the load consumption, the power flow reverses through the MV/LV substations. The reverse power flow impacts mainly on the voltage profile, increasing further the voltage in LV and MV grids. At this regard the Smart Transformer...
Severe distortion will occur in the output current of inverter when grid voltage is unbalanced with harmonics contained. In this paper a scheme of repetitive control for three-phase grid-connected inverters with LCL filter under stationary frame is proposed. The THD of the injected grid current is decreased obviously with the proposed scheme. Two separate decoupled control systems can be achieved...
The asymmetry of the inherent distributed capacitances causes the rise of neutral-to-ground voltage in ungrounded system or high resistance grounded system. Overvoltage may occur in resonant grounded system if Petersen coil is resonant with the distributed capacitances. Thus, the restraint of neutral-to-ground voltage is critical for the safety of distribution networks. An active grounding system...
A new dual-output LLC resonant converter is presented for high power density and high efficiency dual-output application. A new control freedom is provided by replacing two diodes in the secondary-side rectifier with two MOSFETs. Variable frequency modulation plus secondary side phase-shift modulation scheme is adopted to realize precise regulation of both the two outputs simultaneously. Meanwhile,...
Controlled Power Converters are extensively used in industrial applications as they can adapt the electrical energy as required by the application. However, these devices must be properly commutated in order to control voltages and currents. Indeed, power converters are known to be multivariable, coupled, and nonlinear systems; therefore, the control technique needs to be chosen carefully. There are...
For cascaded system, interactions among individually designed power subsystems may cause the instability of the whole system. It has been shown recently that the series-virtual-impedance (SVI) control strategy can stabilize the cascaded system via shaping the load input impedance in a very small frequency to minimize its impact on the original load converter. In this paper, a further investigation...
This paper proposes the use of the feedback-linearization control technique for the regulation of the voltage amplitude and frequency of power-electronic converters. This control strategy linearize the trajectory of a nonlinear system between any two equilibrium points, and thus allowing to use linear control technique. The reference tracking robustness of the proposed control technique is assessed...
This paper presents a novel active synchronization control strategy of multi-bus microgrid based on distributed cooperation technology. The method can reconnect microgrid back to utility grid (UG) seamlessly with sparse communication channels. Through the cross product of voltage vectors in the synchronizer, the frequency and phase of microgrid can track the main grid simultaneously. The voltage differences...
In this paper, a collaborative control scheme is proposed to improve the stability of the microgrid with intermittent renewable energy sources. Different from other cooperative control schemes targeting mostly on regulating the generation side, the proposed operating scheme utilizes all controllable resources in the microgrid, including renewable energy sources (RESs), storage devices, and controllable...
For maximum torque control of induction machines (IM) in flux-weakening region, the following problems exist: 1. In Volts/Hz scalar control mode, a slow frequency ramp time cannot provide sufficient electromagnetic torque, whereas the excessive acceleration leads to overcurrent shutdown and system collapse; 2. In vector control mode, the under-estimated leakage inductance in field-weakening region...
This paper presents an approach to implement the universal flying restart for an induction machine using a frequency search algorithm that determines the rotor speed so that the correct frequency and voltage can be applied to minimize the inrush current during the restart. This method only uses the measured phase current and the motor nameplate parameters, thus making it ideal for use with scalar-controlled...
This paper presents a megawatt scale, medium voltage, medium frequency resonant dual active bridge dc-dc converter operating as a bus-tie converter in a dc distribution network. The high voltage side of the converter is designed using series connected low voltage devices in order to efficiently operate at higher switching frequencies. A combined variable frequency and phase shift control method is...
In this paper, a hybrid control of IPT system is proposed in limited operating frequency range according to coupling coefficients. The coupling coefficient k and self-inductance of pad vary according to misalignment and vertical distance condition in inductive power transfer (IPT) system. Those variation cause change of output voltage and zero phase angle (ZPA) frequency. Proposed method enables the...
To release the “hidden inertia” of variable-speed wind turbines for temporary frequency support, a method of torque-limit based inertial control is proposed in this paper. This method aims to improve the frequency support capability considering the maximum torque restriction of a permanent magnet synchronous generator. The advantages of the proposed method are improved frequency nadir (FN) in the...
Unlike centralized synchronous generator (SG) in conventional power system, distributed micro-sources are parallel connected to neighbors by inverters, which are less-inertia. To improve the transient stability, inverter-based distributed generators (DG) can draw an analogy between the storage and rotor rotational kinetic energy of SG in inertia function. Instead of emulating a fixed virtual inertia,...
Due to variations of misalignment and clearance, the parameters of the contactless transformer (CT) change a lot, creating great challenge in the design and control of the inductive power transfer systems. In this paper, the characteristics of a S/P compensated resonant converter is analyzed by introducing relative self-inductance coefficient and relative mutual-inductance coefficient to describe...
The recently proposed small-AC-signal droop based secondary control is very attractive for microgrids to restore the voltage and frequency of overall system and to share the output power between paralleled distributed generations (DGs). However, the previous work has not discussed the system stability of the novel secondary control method. This paper presents a small-signal model for the microgrids...
High voltage dc (HVDC) systems act as the prevailed solution for transmitting offshore wind energy to onshore main grids. Control of the voltage source converters (VSC) in HVDC systems is decisive for the performance. This paper proposes the control of VSC-HVDC with electromechanical characteristics and unified primary strategy, as a reaction to the updated requirements of the ac grid transmission...
In this paper, a robust decentralized controller is designed for automatic voltage regulator (AVR) and load frequency control (LFC) systems of a generator in an islanded microgrid with multiple distributed generation systems. This control strategy can be readily applied to an islanded microgrid which consists of renewable distributed generation and energy storage systems. The control strategy proposed...
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